This invention relates to NROM devices, and to methods for forming the top oxide on a silicon oxide/silicon nitride/silicon oxide (“ONO”) structure in NROM devices.
Conventionally in manufacture of NROM devices the top oxide of the silicon oxide/silicon nitride/silicon oxide (“ONO”) structure is formed by thermal oxidation of the nitride layer.
However, in conventional processes oxidation of silicon nitride is time-consuming and has a very high thermal budget. In some conventional processes, for example, silicon nitride is oxidized by wet oxidation within a furnace at a temperature of 1000° C. over a time period as long as 60 minutes.
Moreover, the silicon nitride layer in the ONO stack must be made sufficiently thick to allow for consumption of some of the silicon nitride layer during the thermal oxidation step to form the top oxide. Moreover it can be difficult to control the uniformity and thickness of the resulting nitride layer and, accordingly, the resulting NROM cell is less reliable.